With conventional flow cytometers, particles, such as cells, are aligned and carried along ideally in a single file arrangement within a stream of clear fluid, also known as a sheath fluid, to pass before one or more beams of light in an sensing region (or the detection optics) for subsequent detection of various parametric characteristics to classify, categorize, quantify or otherwise detect one or more aspects of the particles. This sheath fluid guides the particles substantially along a desired path such that the particles are at an in-focus position in the sensing region relative to one or more beams of light for subsequent sensing by detectors and automated quantification of cells according to predetermined parametric characteristics. Without the sheath fluid, particles while in the sensing region may not be in a proper in-focus position relative to the beams of light directed into the sensing region so that detection data would be collected regarding out-of-focus and in-focus particles. The detection data collected regarding the out-of-focus particles would lack accuracy and consequently harm the overall integrity of the data collected.
Due to the single-file nature of the particles passing in the sheath fluid, for each particle passing through or in the vicinity of one or more of the light beams in an sensing region, there is generally little or no surrounding particles so that there is little background light scatter or fluorescence to interfere with detection of the predetermined one or more parametric characteristics associated with the particle so that each of the particles can be considered as in-focus while in the sensing region with respect to the one or more beams of light involved. Unfortunately, the need for both clean sheath fluid and a highly stable stream greatly complicates the fluidics of these systems. As a consequence, setup and maintenance of these systems while measurements are being performed is very labor intensive. In addition, related system design such as involving sheath fluid management and sample injection constitute a significant proportion of the complexity found with conventional flow cytometry systems.